O'Day hurt his left hamstring while fielding a bunt on Tuesday night and Gentry sustained a left rib fracture when hit by a pitch in Atlanta on Friday.

It's the second trip to the DL this season for O'Day, who missed a month with a hyperextended elbow.

This injury could also result in a lengthy absence. Manager Buck Showalter said, "Not sure we can put a timeframe on it. It's pretty sore."

The sidearmer is 0-2 with a 3.60 ERA.

Gentry is batting .244 with a team-high 10 steals.

Baltimore recalled utility man Steve Wilkerson and right-hander Jimmy Yacabonis from Triple-A Norfolk. Wilkerson made his major league debut last week, and Yacabonis is expected to start Thursday against Seattle in place of Dylan Bundy, who went on the disabled list Tuesday.